Processes for the crystallisation of water-soluble compounds from an aqueous solution are energy and capital intensive. An example of a process wherein such crystallisation plays an important role is the process for producing crystalline sucrose from sucrose-containing biomass, such as for example sugar beets including tropical beet, and sugar cane and from sugar palm juice.
In the conventional process for the manufacture of crystalline sucrose from sugar beets, the sucrose is extracted from comminuted beet strips with water in an extractor that is commonly called a diffuser. The sucrose-containing liquid that exits the diffuser is known as raw juice and is subjected to a carbonatation process in order to remove impurities that could frustrate the crystallisation process. Examples of such impurities are multivalent anions (e.g. sulphate, phosphate, citrate and oxalate), proteins, amino acids, saponins, pectins and monosaccharides such as glucose and fructose. The so-called thin juice that is obtained after carbonatation is evaporated to obtain a thick juice with a sucrose content of approximately 60%. The thick juice is fed to a crystalliser where it is seeded with fine sucrose crystals and further concentrated under vacuum to form crystallised sucrose. Liquid is removed from the sucrose crystals formed by centrifugation.
The conventional process is optimised towards the yield of crystalline sucrose from the biomass.
Disadvantages of the conventional process are that the process is highly energy and capital intensive and that costs to transport the voluminous beets to the sucrose production site are high. Moreover, the conventional process is directed towards optimization of the yield of crystalline sucrose, a product that is currently facing lower selling prices.